Yambo Community Forum

Hi,

I have gone through the tutorials of yambo and learned how to calculate optical properties. I have seen some examples of 2D and 3D materials e.g hBN, MoS2, silicon. However, If we apply bias voltage on materials, I think it will affect on fermi energy. So, is it possible to calculate optical properties e.g. dielectric function, under the application of bias voltage on 2D/3D materials?

Thank you
Best Regards
Ehsanul Azim
Masters student
Mechanical Engineering
University of Texas Rio Grande Valley

Dear Ehsanul,

it is possible e.g. by applying a saw-like potential in Quantum Espresso in a 2D material in the direction perpendicular to the plane of the material. Yambo will read the generated electronic structure and the Fermi energy will be calculated accordingly.

Best,
Daniele

Hi Professor Daniele,

Thank you for your reply. Would you please little bit elaborate the 'saw-like potential in Quantum Espresso"? However, instead doing the dielectric constant, Would it be possible to find out conductivity /sigma(omega) using yambo under the bias voltage?

Thank you again.

Best Regards
Ehsanul Azim
Masters student
Mechanical Engineering
University of Texas Rio Grande Valley

Hi Professor Daniele,

I have seen some papers related to saw-tooth potential in QE, I am studying it. If you can just answer the 2nd question about frequency dependent conductivity, that would be very helpful for me.
Thank you

Best Regards
Ehsanul Azim
Masters student
Mechanical Engineering
University of Texas Rio Grande Valley

Dear Ehsanul,

you can have a look at the quantum espresso documentation:
https://www.quantum-espresso.org/Doc/IN ... tml#idm147
in particular, the variable tefield and related keywords. Activating this variable, a saw-like potential simulating an electric field
is added to the bare ionic potential. Once the electronic structure is calculated in presence of this external potential, you can use Yambo to calculate the response function and related quantities. Please note that the dielectric is not well-defined in a 2D material, and you should look at the polarizability.

Another way to consider a homogeneous external electric field in QE is using "lelfield", through the modern theory of the polarization. This can be used also for a periodic system, but I do not have experience on that for a Yambo calculation on top of this.

Best,

Daniele